Fission fragment K x-ray emission and nuclear charge distribution for thermal neutron fission of 233U, 235U, 239Pu and spontaneous fission of 252Cf

doi:10.1016/0375-9474(71)90297-1

Nuclear Physics A

Volume 177, Issue 2, 20 December 1971, Pages 337-378

https://doi.org/10.1016/0375-9474(71)90297-1 Get rights and content

Abstract

The emission of K X-rays by fission fragments within ≈ 1 nsec after fission has been studied as a function of fragment mass and nuclear charge for thermal neutron-induced fission of ²³³U, ²³⁵U, ²³⁹Pu and spontaneous fission of ²⁵²Cf. This work is based on a simultaneous measurement of the fragment kinetic energies to obtain the fragment masses and high-resolution measurement of the characteristic energy spectra of the K X-rays emitted by the fragments to determine their nuclear charges. For all four fissioning systems the K X-ray yields per fragment were found to be strongly dependent on nuclear structure. Near closed nuclear shells the K X-ray yields for odd-Z nuclei are enhanced relative to even-Z nuclei. Away from closed shells the K X-ray yields increase rapidly with Z and A, and the odd-even Z-fluctuations diminish. With an approximate parameterization for the dependence of K X-ray yields on Z andA, the average nuclear charges of the primary fragments represented as a linear function of their pre-neutron-emission mass (charge division) and the width of the charge distribution about the average values (charge dispersion) were obtained. The linear charge division functions obtained in this work are in good agreement with existing radiochemical data and with recent β-decay chain-length measurements. The average charge dispersion (before neutron emission) found in this work for ²³⁵U(n, f) (σ_z = 0.40 ±0.05 charge units) is narrower than the charge dispersion (0.56±0.06) determined radiochemically (after neutron emission).

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Total kinetic, excitation energy and neutron multiplicity distribution of californium isotopes
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The mean total kinetic energy as a function of fission fragments, <TKE>(A), is calculated for neutron-induced fission of ^{247,249,251,253,255}Cf, as well as for spontaneous fission of ^{248,250,252,254}Cf using the scission point model. A comparative analysis is performed between the calculated results and existing experimental data. Investigation into the behavior of <TKE>(A) is conducted, particularly focusing on intermediate and heavy actinides. While nuclear and Coulomb energy evaluations suffice for estimating <TKE> values in light actinides, this approximation proves inadequate for evaluating TKE values for intermediate and heavy actinides. Additionally, an evaluation is made of the total excitation energy as a function of fission fragments, <TXE>(A), concerning spontaneous fission in ^247−254Cf. It is found that TXE values sharply increase near the symmetric region across all isotopes and exhibit a gradual increase in heavy fission fragments. Furthermore, an exploration of the total neutron multiplicity as a function of fission fragments, $ν_{T} (A)$ , is conducted for ²⁵²Cf fission using two methods. The $ν_{T} (A)$ results obtained through these methods are compared with experimental data, and $ν_{T} (A)$ is estimated for unmeasured californium isotopes. The average neutron emission per fission event, $\bar{ν} (A_{i})$ , is then calculated for spontaneous fission of ²⁵¹Cf and ²⁵³Cf, yielding values of 3.46 and 3.59, respectively.
Fission fragment decay simulations with the CGMF code
2021, Computer Physics Communications
The CGMF code implements the Hauser-Feshbach statistical nuclear reaction model to follow the de-excitation of fission fragments by successive emissions of prompt neutrons and γ rays. The Monte Carlo technique is used to facilitate the analysis of complex distributions and correlations among the prompt fission observables. Starting from initial configurations for the fission fragments in mass, charge, kinetic energy, excitation energy, spin, and parity, Y(A,Z,KE,U,J,π), CGMF samples neutron and γ-ray probability distributions at each stage of the decay process, conserving energy, spin and parity. Nuclear structure and reaction input data from the RIPL3 library are used to describe fission fragment properties and decay probabilities. Characteristics of prompt fission neutrons, prompt fission γ rays, and independent fission yields can be studied consistently. Correlations in energy, angle and multiplicity among the emitted neutrons and γ rays can be easily analyzed as a function of the emitting fragments. In its current version, CGMF is limited to certain spontaneous fission reactions on Pu and Cf isotopes, as well as neutron-induced fission reactions up to 20 MeV on U, Np, and Pu isotopes.
Program Title: CGMF 1.1
CPC Library link to program files: https://doi.org/10.17632/jrtt73npzw.1
Licensing provisions: BSD-3 clause
Programming language: C++
Nature of problem: Modeling of fission fragment decay
Solution method: Monte Carlo implementation of the Hauser-Feshbach statistical theory of nuclear reactions to describe the de-excitation of fission fragments on an event-by-event basis.
Additional comments including restrictions and unusual features: spontaneous fission reactions for ^{238,240,242,244}Pu and ^252,254Cf; neutron-induced fission reactions from thermal up to 20 MeV for n+^{233,234,235,238}U, n+²³⁷Np, and n+^239,241Pu. Binary fission only (no ternary fission).
Fission fragment atomic number measurements using Bragg detectors
2020, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
A Bragg detector with a Frisch grid and 1 metre-long time-of-flight section with microchannel plate assemblies was characterized at the Lohengrin fission fragment separator at the Institut Laue-Langevin (ILL) by measuring ²³⁵U fission fragments of selected masses and energies at the Lohengrin focal plane. The aim of the measurements was to investigate the response of Bragg detectors to differing nuclear charge states. Energy-loss and a signal-risetime dependent parameters were defined and extracted from the accumulated signal pulse shapes, and their behaviour as a function of fragment velocity was investigated. The experimental results are compared to a SRIM-2013 simulation. Measurements of fission fragment ranges in isobutane are presented. Average proton numbers for measured fragment masses were identified and could be resolved by the parameters, which exhibited monotonic variation with charge. The results differed from SRIM both in trends and in values, with SRIM simulations exhibiting non-monotonic behaviour with proton number.
Charge distribution of light mass fission products in the fast neutron induced fission of 232Th, 238U, 240Pu and 244Cm
2017, Applied Radiation and Isotopes
Citation Excerpt :
The charge distribution studies in the neutron induced fission of actinides have been carried out by using different physical (Reisdorf et al., 1971; Cheifetz et al., 1971; Brissot et al., 1975, 1977; Balestrini et al., 1979; Shmid et al., 1981; Mariolopoulos et al., 1981; Djebara et al., 1984, 1989; Datta et al., 1988; Siegert et al., 1976; Clerc et al., 1975; Lang et al., 1980; Bocquet et al., 1980; Schmitt et al., 1984; Quade et al., 1988; Rochman et al., 2002; Boucheneb et al., 1989, 1991; Schillebeeckx et al., 1994; Medkour et al., 1997) and radiochemical technique (Wahl et al., 1969; Notea, 1969; Balestrini and Forman, 1974; Wolfsberg, 1975; Amiel and Feldstein, 1975; Amiel et al., 1977; Izak-Biran and Amiel, 1977, 1978; Gäggeler and von Gunten, 1978; Erten and Aras, 1979; Wahl, 1980, 1988; Dickens and McConnell, 1981a, 1981b, 1983; Erten et al., 1982; Meixler et al., 1983; Dobreva and Nenoff, 1984; Haddad et al., 1987, 1988, 1989; Srivastava and Denschlag, 1989; Hentzschel and Denschlag, 1990; Naik et al., 1997, 1998, 2003, 2004). Except few (Reisdorf et al., 1971; Cheifetz et al., 1971; Brissot et al., 1975, 1977; Balestrini et al., 1979; Shmid et al., 1981), rest of the physical techniques (Mariolopoulos et al., 1981; Djebara et al., 1984, 1989; Datta et al., 1988; Siegert et al., 1976; Clerc et al., 1975; Lang et al., 1980; Bocquet et al., 1980; Schmitt et al., 1984; Quade et al., 1988; Rochman et al., 2002; Boucheneb et al., 1989, 1991; Schillebeeckx et al., 1994; Medkour et al., 1997) are used only for light mass fission products, in the thermal neutron induced fission of 229Th to 249Cf and in the spontaneous fission of 252Cf. On the other hand, radiochemical separation in combination with γ-ray spectrometric technique (Wahl et al., 1969; Notea, 1969; Balestrini and Forman, 1974; Wolfsberg, 1975; Amiel and Feldstein, 1975; Amiel et al., 1977; Izak-Biran and Amiel, 1977, 1978; Gäggeler and von Gunten, 1978; Erten and Aras, 1979; Wahl, 1980, 1988; Dickens and McConnell, 1981a, 1981b, 1983; Erten et al., 1982; Meixler et al., 1983; Dobreva and Nenoff, 1984; Haddad et al., 1987, 1988, 1989; Srivastava and Denschlag, 1989; Hentzschel and Denschlag, 1990; Naik et al., 1997, 1998, 2003, 2004) is used for both light and heavy mass fission products in the thermal neutron induced fission of 229Th to 249Cf and in the spontaneous fission of 252Cf.
Fractional cumulative yields (FCY) of various light mass fission products in the fast neutron induced fission of ²³²Th, ²³⁸U, ²⁴⁰Pu and ²⁴⁴Cm have been determined by using the off-line γ-ray spectrometric technique. From present and literature data, width of isobaric charge distribution (σ_Z), the most probable charge (Z_P) and the experimental charge polarization (∆Ζ_EXPT) as a function of fragment mass were deduced. The ∆Ζ_EXPT values from the present work for light mass chains and earlier work for heavy mass chains show oscillating nature due to nuclear structure effect. The ∆Ζ_MPE values based on minimum potential energy surface were theoretically calculated, which shows a systematic decrease trend with the approach of symmetric split due to the liquid drop behaviour of the fissioning nucleus.
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2017, Energy Procedia
Prompt neutrons emitted from fission fragments of actinides show a specific induced-energy dependence. The mass distribution of prompt neutrons emitted from light fragments are independent of induced energies, while the number of prompt neutrons originating from heavy fragments increases with increasing induced energy. The understanding of the mechanism of this behavior has been a long standing problem, and cannot be solved unless we assume very artificial conditions such as fragment-mass dependent temperatures. Therefore, the neutron multiplicity has been used as fitted information in major models for prompt neutron spectra. In this paper, we evaluate the prompt neutron multiplicity as a function of the fission-fragment product of the n-induced fission of U-235 based on the fission configuration derived from the Langevin equation. We found that the charge polarization, which is the deviation from the unchanged charge distribution (UCD) assumption, can directly produce the specific induced-energy dependence of prompt neutrons without extra assumptions.
Prompt Fission Neutron Spectra of Actinides
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^‡: Work performed undeer the auspices of the US Atomic Energy Commission.

^†: Nuclear Physics Laboratory, University of Washington, Seattle, Wash.

^††: Chemistry Department, University of Michigan, Ann Arbor, Michigan.

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Nuclear Physics A

Abstract

References (54)

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thesis

J. Chem. Phys.

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Cited by (135)

Total kinetic, excitation energy and neutron multiplicity distribution of californium isotopes

Fission fragment decay simulations with the CGMF code

Fission fragment atomic number measurements using Bragg detectors

Charge distribution of light mass fission products in the fast neutron induced fission of <sup>232</sup>Th, <sup>238</sup>U, <sup>240</sup>Pu and <sup>244</sup>Cm

The charge polarization and its impact on prompt fission neutron multiplicity

Prompt Fission Neutron Spectra of Actinides